Re: Namespaces,W3C XML Schema (was Re: ANN: SAX FiltersforNamespaceProcessing)

[Ronald Bourret <rpbourret@rpbourret.com>]

Elliotte Rusty Harold wrote:
> 
> At 10:25 PM -0700 8/21/01, Ronald Bourret wrote:

> >The use isn't theoretical. Witness all the products that generate
> >classes from XML Schemas.
> >
> 
> And witness all the people using these products NOT. I classify this
> stuff along with tree-based XML editors and binary variants of XML as
> something that gets reinvented several times a month without any actual
> market demand.

I don't have any hard statistics, but I did notice that the Castor
mailing list had roughly 11,000 messages in the last year and a half.
That's probably not just the developers talking to themselves :)

I'm also hard put to imagine that the average programmer really wants to
manipulate business data in the form of an XML document. It's
inefficient and error prone. My guess is that most people who are using
XML documents to exchange data and who are not immediately storing that
data in the database are marshalling that data to internal data objects.
It also wouldn't surprise me if most of the code to do this today was
custom, but that's not surprising given the newness of most of these
products. (The oldest -- Quick and Castor -- don't seem to spend much
time marketing themselves. My guess is that JAXB will change that.)

> On the other hand, over the last three years as I've taught developers
> about DTDs, almost invariably the first question is "How do I say that an
> element contains an int?" and the second question is usually ""How do I
> say that an element contains a year since 1969?" or some variant thereof.

Not surprising, for two reasons. First, as we both agree, far more
people will use schemas for validation than for other purposes. Second,
if you're teaching developers about DTDs, they don't yet know enough to
say, "Hmmm. I really don't want to manipulate my parts list as an XML
document."

> >If you count applications, validators are a minority.
> 
> I count people as worth more than programs.

Oh, yeah, lay that on me. Next you'll ask when I stopped beating my wife
:)

> >> In validation, we need local types (if not necessarily unqualified
> >> local types) because the W3C XML Schema Language confuses the two
> >> separate issues of typing and constraints checking, especially when
> >> it comes to complex types. I don't want to see any prohibition on
> >> local types enshrined as a best practice, or otherwise deprecated.
> >
> >Could you explain this further? Isn't constraints checking either (a)
> >the checking of data against types, or (b) the definition of domains for
> >a given type? (I suppose this also depends on what you mean by "type".)
> >
> 
> If you view restrictions as subclasses, then you can do it all as
> typing. However, this is problematic in a lot of the naive approaches
> people are taking. For instance, what's an appropriate subclass of
> int in Java or C++?

Got it. Thanks.

-- Ron